Image evaluation methods of this type and the corresponding objects (data medium with computer program, programmed computer) are known.
Thus, for example, an image evaluation method of this type is known from the technical article “Quantitative Analyse von koronarangiographic Bildfolgen zur Bestimmung der Myokardperfusion” [Quantitative analysis of coronary angiographic image sequences for determining myocardial perfusion] by Urban Malsch et al., which appeared in “Bildverarbeitung fur die Medizin 2003—Algorithmen—Systeme—Anwendungen” [Image processing for medicine 2003—algorithms—systems—applications], Springer Verlag, pages 81 to 85. With this image evaluation method, a computer uses the projection images to determine a two-dimensional evaluation image, which comprises a plurality of pixels, and outputs the evaluation image to a user via a display device. The pixels of the evaluation image correspond to those of the projection images. The computer uses the temporal profile of the pixel values of the projection images to assign a pixel value to the pixels of the evaluation image, the pixel value being characteristic of the time of maximum contrast change.
The doctrine of the above-mentioned technical article is described in the context of angiographic examinations of the coronary arteries of the human heart. This type of examination is one of the most important diagnostic tools in cardiology today. Additional information such as the determination of flow velocity or myocardial perfusion is further information which can in principle be obtained by means of angiography. The essential diagnostic evidence here is the perfusion of the cardiac muscle.
Today, a number of other non-invasive methods of examination such as PET, SPECT, MR or contrast-medium-aided ultrasound have also become established. These methods of examination offer the facility for quantifying, in addition to other parameters, the perfusion status of the myocardium. These methods are generally applied in stable angina pectoris cases or in order to assess the risk after a myocardial infarction.
For an assessment of the therapeutic outcome of an intervention, it would therefore be advantageous to be able to monitor the improvement in perfusion and/or the occurrence of microembolization and microinfarctions during the actual intervention. It would consequently be advantageous if quantification of perfusion were added to the other diagnostic parameters in the catheter laboratory, as this would make it possible to obtain all relevant information in one examination and thus to achieve an improvement in the monitoring of treatment.
Quantification of the supply of blood to the myocardium by means of angiographic methods is however problematic, since the angiographically observable cardiac vessels have a diameter of just under a millimeter or more. These observable vessels terminate in millions of tiny capillary vessels, which have diameters of only a few micrometers. The flow dynamics and distribution in the capillary vessels are ultimately determined by the blood supply to the cardiac muscle. Drawing conclusions from the macroscopic supply of blood as to the dynamics of the supply of blood in the capillary vessels is, strictly speaking, inadmissible, even though it is often done.
In order to capture the supply of blood to the myocardium, various methods are known, in particular contrast echocardiography, magnetic resonance tomographic diagnostics and SPECT.
In order to make the blood flow dynamics in large vessels and in the capillary vessels measurable and thereby comparable, various gradation systems are known which divide up the continuum of conditions into discrete classes. Some of these classifications describe the macroscopic circulation of blood, others the circulation of blood in the capillaries. The most commonly used classifications were drawn up by the scientific organization “Thrombolysis in Myocardial Infarction” (TIMI). These classifications are deemed to be the standard. In multi-center studies in which reproducible and comparable results are of particular importance, the TIMI classifications are frequently used. The classifications are complex and can be applied only in a time-consuming manner. They are therefore not generally used in routine clinical work.
By far the most frequently used method in the prior art is the visual assessment of “myocardial blush” on a screen. This procedure is often used for multi-center studies. A prerequisite for this procedure is that the angiographic recording is long enough, in order to be able to see the input and washout of the contrast medium. The visual assessment requires a lot of experience and is in practice carried out only by TIMI-blush experts, as they are known.
Various procedures are also known, in which an attempt is made to carry out this subjective and personal visual assessment with the aid of computers. An example is to be found in the above-mentioned technical article by Urban Malsch et al.
The procedure in the above-mentioned technical article represents a good initial approach but still displays shortcomings. For example it is particularly necessary to identify the vessels of the vascular system in the projection images in order to mask out these vessels when evaluating the “myocardial blush”. It is also necessary in the case of the procedure in the technical article to work with DSA images. This gives rise to a significant risk of artifacts, to avoid which computation-intensive methods are in turn required in order to compensate for motion.
Image evaluation methods for two-dimensional projection images are also described in the German patent application DE 10 2005 039 189.3. At the date of filing of the present invention said patent application is not yet available to the public and therefore does not represent a general prior art. Said patent application is only to be taken into account in the context of the examination as to novelty in the German procedure for granting patents.